Engine cooling fan control systems have been used on various vehicles for thermal management of the engine by turning on the engine cooling fan when the engine needs to be cooled. Cooling is necessary to prevent overheating of the engine under various different speeds and loads. In the case of an internal combustion engine, the amount of heat that needs to be rejected typically requires that the engine have its own cooling system, either air cooled or liquid cooled. While air cooling is adequate for smaller engines, larger engines typically require liquid cooling.
The liquid coolant is circulated through passages in the engine during which heat is absorbed from the engine by conduction. The liquid coolant runs a loop between the engine and a heat exchanger, i.e. a radiator. The heat from the liquid coolant absorbed from the engine is reabsorbed by the radiator.
In situations where the ram air for forcing flow of ambient air through the radiator is not enough for adequate heat rejection, an engine cooling fan associated with the radiator is used to force ambient air through the radiator.
An electro-mechanical device such as a clutch is a type of interface used between the engine and the engine cooling fan. An electrical signal, usually developed via suitable algorithms in the processor of an electric engine control system engages and disengages the clutch to connect and disconnect the cooling fan respectively.
Considerations of fuel economy, noise and temperature control have resulted in various forms of electric control of engine cooling fans. The intent of some electrical control strategies is to selectively connect and disconnect the engine cooling fan according to engine cooling needs. This type of fan control is sometimes called ‘On-Off’ control. This selective control ensures that the fan is not being used wastefully while attaining adequate cooling.